While Gareth Morgan's gripe about cats had more to do with the threat to native birds, scientists say there may be another reason not to trust your favourite feline.

Auckland University scientists have found acute toxoplasmosis, an infectious disease carried by cats, may be a much more serious illness for humans than previously thought.

Recent studies have shown the illness, which releases dopamine into the brain, can be very severe and disabling. About 40 per cent of Kiwis are infected with toxoplasmosis at some time in their lives and it cannot be cured.

"While chronic toxoplasmosis has been shown to have a strong association with conditions affecting the brain such as schizophrenia, and with suicide and self-harming behaviour, the disease in its acute phase has usually been seen as a benign, trivial and self-healing illness," Associate Professor Mark Thomas from the Department of Molecular Medicine and Pathology said.

"We were surprised, when the results came in, to discover how common it was for patients to report significant and prolonged symptoms such as impaired memory and concentration, headaches and extreme fatigue."

The study was unique in its focus on people in the community rather than in hospital.

Of the 31 patients who completed the questionnaire, 90 per cent reported fatigue, 74 per cent reported headaches and 52 per cent found they had difficulty in concentrating.

Sixteen of the 31 had aches in their muscles and 12 had fever, with one person briefly admitted to hospital because of sweats, muscle aches and elevated heart rate.

While Thomas acknowledged the respondents may have been those worst affected, he believed the results would be of interest to doctors throughout the world since they contradicted the previous misconceptions about the acute phase of the illness and gave a deeper understanding of what patients may be experiencing.